What a fun chance for you to be creative and write about something interesting. Of course, you and I might have very different ideas about what is "fun," but this will give you some things to think about, anyway.
How about taking a look at the wacky things people do to treat their pets as human beings. Spa treatments, special foods, amazing "houses," and outrageous burials when they die are some things to consider.
Phobias are always interesting both to study and to hear about. Perhaps you can choose several phobias within one category of fears or three different categories of fears. Perhaps a more researched approach would be to explain what phobias are, what causes them, and how to cure them. You could certainly use examples of different fears and phobias throughout the presentation.
Food is always good for an interesting topic. Explore the types of foods one country would never eat but are seen as a delicacy or as a common food in other countries.
If you want something a little more controversial/persuasive, decide whether you believe "regular" people should be able to own exotic pets, such as tigers, large snakes, and large apes. Or, on the other side of things, whether keeping animals caged in a zoo for public display is inhumane.
If you are looking for something a bit more informational, research the differences between the Amish and the Mennonites, as they are generally seen as one entity but are not. Or research some of the more outlandish ways people have chosen to be buried--and some of the more eco-friendly ways in which some people are being buried.
Changes in clothing is also a fun one to research and hear about. Do you know, for example, when women first started wearing pants and why?
During World War I, women wore their husbands' (suitably altered) trousers while they took on jobs previously assigned to men, and increasingly wore trousers as leisurewear in the 1920s and 30s.
Truly, anything will work for a presentation like this. If your audience is your peers, you can make one very good assumption: if the subject interests you, it will probably interest them, as well. Think about doing a little research on something you have always wondered about, and the odds are good that others in your class have also wondered about it and will be interested.
As far as making the presentation a bit more formal, that can be most easily done by creating a clear and focused outline from which to present. If you have an effective organization, you will be able to present even really fun information in a professional way. Good luck and have fun!